A couple of months ago, AbbVie ($ABBV) pointed to its late-stage cancer drug venetoclax (ABT-199) as a prime reason it was willing to pay a dizzying $21 billion in order to acquire Imbruvica-maker Pharmacyclics. Matching the blood cancer blockbuster with its experimental therapy would help amp up its market reach, said AbbVie. And the FDA has now boosted that argument with its breakthrough therapy designation (BTD) for venetoclax, possibly opening the door to a swifter approval path.

The FDA handed out BTD bragging rights to the drug for chronic lymphocytic leukemia (CLL) for patients with the 17p deletion genetic mutation. Roughly 3% to 10% of all first-line patients have that mutation, while up to half of treatment-resistant patients are in the group.

Late last year at ASH the drug, which is partnered with Roche ($RHHBY), continued to impress analysts with promising data. Investigators noted an 88% overall response rate and a number of remissions among a group of relapsed or refractory CLL patients taking a combination of venetoclax andRituxan. And the significance didn't escape a group of prominent analysts who are closely watching the drug's progress in the clinic.

Opinion leaders in the field "praised the impressive number of complete remissions and MRD negative remissions, noting that this could represent a "new paradigm" where disease does not recur as soon as therapy is stopped and suggesting that a discontinuation trial could make sense, which would not be possible with other agents," noted Bernstein's Geoffrey Porges at the time.

Goldman's Jami Rubin called the drug a potential "best-in-class" remedy.

Venetoclax works by inhibiting the BCL-2 protein, which prevents apoptosis, or cell death. That makes it a natural combination therapy at a time when drugmakers have been rapidly accelerating their investments in oncology. It's particularly important for AbbVie, which sees the drug as a key opportunity to diversify beyond its megablockbusterHumira.